Switching power supply circuit

Abstract

A switching power supply circuit reduces the capacity of the capacitor on the load side, reducing its size, weight, and cost. The switching power supply circuit has a pair of diodes connected in series, a pair of MOSFETs connected in series, a pair of capacitors connected in series, a snubber capacitor connected in parallel with the pair of diodes, the pair of MOSFETS, and the pair of capacitors. The circuit can include a pair of additional capacitors, connected respectively in parallel with the MOSFETS, to allow the MOSFETs to execute a zero-voltage switching. The circuit also includes an AC input terminal connected to the mutual connection point of the pair of diodes, a transformer including a primary winding having one end connected to the mutual connection point of the pair of MOSFETS, and the other end connected to the mutual connection point of the pair of capacitors. The primary winding has a center tap connected to another AC input terminal.

What is claimed is:  
     
       1. A switching power supply circuit comprising: 
       a transformer having a primary winding with a center tap and a secondary winding;  
       a pair of diodes connected in series;  
       a pair of switching devices connected in series;  
       a pair of capacitors connected in series;  
       a snubber capacitor;  
       a first AC input terminal connected to both of the pair of diodes; and  
       a second AC input terminal connected to the center tap of the primary winding,  
       wherein the snubber capacitor, the pair of diodes, the pair of switching devices, and the pair of capacitors are connected in parallel,  
       wherein one end of the primary winding is connected to both of the pair of switching devices, and  
       wherein the other end of the primary winding is connected to both of the pair of capacitors.  
     
     
       2. The switching power supply circuit according to  claim 1 , further including a rectifying circuit connected to the secondary winding of the transformer. 
     
     
       3. A switching power supply circuit comprising: 
       a switching means for converting a single-phase AC input voltage to a high-frequency AC voltage;  
       a transformer for insulating the high-frequency AC voltage, wherein the transformer comprises a primary winding having a center tap and a secondary winding,  
       a rectifying circuit for rectifying the insulated high-frequency AC voltage to feed DC electric power to a load;  
       a first circuit comprising two diodes connected in series;  
       a second circuit comprising two switching devices connected in series;  
       a third circuit comprising a first capacitor and a second capacitor connected in series;  
       a snubber capacitor, wherein the snubber capacitor, the first circuit, the second circuit and the third circuit are connected in parallel;  
       a first AC input terminal connected to a common connection point of the two diodes in the first circuit; and  
       a second AC input terminal connected to the center tap of the primary winding,  
       wherein one end of the primary winding is connected to the common connection point of the switching devices of the second circuit,  
       wherein the other end of the primary winding is connected to the common connection point of the first capacitor and the second capacitor of the third circuit, and  
       wherein the rectifying circuit is connected to the secondary winding of the transformer.  
     
     
       4. The switching power supply circuit according to  claim 3 , further including at least one capacitor connected in parallel with at least one of the switching devices, wherein the at least one capacitor allows at least one of the switching devices to execute a zero-voltage switching. 
     
     
       5. The switching power supply circuit according to  claim 3 , wherein the switching power supply circuit adjusts an ON-OFF duty ratio of one of the switching devices to regulate the current of the AC input voltage, and the switching power supply circuit adjusts the operating frequency of the other of the switching devices to regulate the DC electric power. 
     
     
       6. The switching power supply circuit according to  claim 4 , wherein the switching power supply circuit adjusts an ON-OFF duty ratio of one of the switching devices to regulate the current of the AC input voltage, and the switching power supply circuit adjusts the operating frequency of the other of the switching devices to regulate the DC electric power.